1. Field of Invention
The present invention relates to digital camera modules used in digital equipment and mobile phones, and in particular to low power consumption actuators to improve longevity of battery power.
2. Description of Related Art
Today there are various types of actuators used to perform auto focus (AF), zoom and camera shutter functions. In traditional digital still cameras (DSC) stepper motors are being used for actuator functions. These stepper motors require a relatively large current in the range of 100 mA to 200 mA that provide a drain on the operating life of the batteries used. To facilitate a long operation time, large batteries are used.
In FR 823395 (Lavet) a low energy stepper motor is directed to horological devices such as watches and clocks. U.S. Pat. No. 2,986,683 (Lavet) is directed to drive wheels particularly applicable to timing instruments. U.S. Pat. No. 3,667,210 (Meitinger) is directed to a horological instrument that includes an oscillator such as a balance wheel. The oscillator comprises a conductive ring that is induced with current by mutual induction from a fixed coil. In U.S. Pat. No. 4,504,132 (Martin et al.) a multifunction electromagnetic actuator is directed to controlling exposure and focus in a photographic camera. U.S. Pat. No. 4,563,604 (Xuam) is directed to an electromagnetic stepping motor comprising two rotors coupled to a common transmission wheel to permit decreased size or decreased energy consumption for horological applications.
U.S. Pat. No. 5,206,983 (Guckel et al.) is directed to a micromechanical device formed on a substrate using X-ray lithography process to form a rotating micromotor which is driven magnetically. In U.S. Pat. No. 5,349,574 (Edwin et al.) a horological movement is directed to a shaft guide where the guide is composed of three pieces sandwiched on one another to receive a control member. In U.S. Pat. No. 5,685,062 (McCarthy et al.) a method of fabrication is directed to a planar micro-motor suited for batch method of fabricating multiple planar stepper micro-motors from a single substrate wafer. U.S. Pat. No. 5,838,080 (Couderchon et al.) is directed to a stepper motor comprising a rotor, stator, a coil with a magnetic core in which the stator consists of a soft magnetic alloy.
U.S. Pat. No. 5,918,078 (Imura et al.) is directed to a lens driving device that includes an operation ring rotated by a motor for automatic focusing. In U.S. Pat. No. 6,301,441 (Kato) a lens driving device is directed to focusing the lens of a camera using an AF motor. In U.S. Pat. No. 6,430,368 (Hata) an auto-focus apparatus is directed to a focusing device that has a first mode of a fine step interval for AF evaluation and a second mode of a course step interval for obtaining a rough in-focus position. U.S. Pat. No. 6,614,998 (Senba et al.) is directed to an auto-focus device that determines a plurality of positions of a lens group for focusing on a plurality of subjects using an AF motor the lens group or the imaging surface of a CCD device. A paper, “Micromotor Based on Film Permanent Magnets”, P. Meneroud et al., Actuator 2004, 9th International Conference on New Actuator, pp491-494, 14-16 Jun. 2004, Bremen, Germany; is directed to a design for a single step micro-motor where the rotor has been optimized to induce the greatest magnetic energy using film permanent magnets.
FIG. 1 is a schematic diagram of a digital camera unit of prior art. An image is focused onto a CMOS/CCD imager sensing array 10 by a set of zoom lens 11 and auto focus lens 12. A set of motors 13 are used to actuate a shutter 14 and adjust the set of zoom lens 13 and the set of auto focus lens 12. The current requirement of the set of motors 13 necessitates the use of the motor driver circuits 15. The motor driver circuits are controlled by the image processing circuitry 16, which requires an input from zoom position 17, AF (auto focus) position 18 and sensor control 19 to control the movement of the motors 13 and provide a focused image onto the CMOS/CCD imager sensing array 10. The current requirement of the motors 13 provides a large drain on the power supply of the battery of the digital camera unit, and extra circuitry is required to provide position information of the zoom lens 11 and the auto focus lens 12.
In the mobile phone market, digital camera modules are being integrated into mobile phone handsets. This emerging new market of mobile phones comprising digital camera functions compete with low to midrange DCS market and challenges the capability of power consumption to provide an adequate battery life during operation, which in turn challenges low power consumption of the needed actuator elements.
In the watch industry precision, compact and low power actuators have been implemented using a Lavet motor concept. The Lavet type motors are capable of driving watch mechanisms with very low voltages and consuming very low current. This is a result of the Lavet style motors being active only when a step is performed, which leads to a very low power consumption resulting in battery life up to five years. Appling the Lavet concept to actuators in motorized camera modules produces lower power consumption along with a smaller size and simple electronic control, wherein the actuator power consumption is approximately fifteen times lower with approximately ten times lower current consumption at a one and a half times lower voltage. This leads to operating product containing digital cameras longer than product using conventional actuator and is particularly important to the mobile phone market.